Ampthill Clay

The Ampthill Clay was deposited about 155 million years ago, after the Oxford Clay.  It was named after the village of Ampthill in Bedfordshire where the clay was exposed.  In 1970 excavations for the sewage treatment works at Ampthill exposed the clay, it was also exposed in local railway cuttings.  In other areas of the country it has been called by other names, often linked to placed where it was found.  In Bedfordshire exposures of Ampthill Clay are few at present.  In many areas it was weathered away completely during the late Jurassic and early Cretaceous.  This is why in some areas Cretaceous rocks rest directly on the Oxford Clay.  Most of the Ampthill Clay fossils in Bedford Museum have been found in the boulder clay.  They were washed out of the Ampthill Clay during the Ice Age and re-deposited in layers of gravel and boulder clay.  Fossils that have been moved in this was are called derived fossils.

In some areas deposits about the same age as the Ampthill Clay were formed in shallow waters containing corals.  This led to the name Corallian for rocks of this age.

The Kimmeridge Clay was deposited next.  It was formed in deeper water as sea levels were rising.  Derived Kimmeridgian fossils can be found in the base of the Lower Greensand.

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